Filters that are used to filter air for use in clean rooms commonly are referred to as "HEPA" filters, and are capable of removing even very small dust particles and microorganisms from the air flow. HEPA filters, supplied commercially in the form of porous sheets or plates, are common to the industry, and need not be described further. Clean rooms often have filter assemblies including housings containing HEPA filters installed in ceilings, with the filtered air thus issuing into clean rooms exiting through exhaust ports located generally at floor level around the peripheries of the rooms.
It is generally desirable to locate the lighting fixtures for clean rooms at or near the ceilings. Inasmuch as filter sheets or plates such as the HEPA filters are light-absorbing, only a portion of the light emitted by lights carried beneath the filters is useable. As a result, high-powered lights must be used so that the light which reaches the work level is sufficiently intense to enable workers to appropriately perform their duties. As a result, much energy is wasted in lighting such rooms.
The air issuing from ceiling-mounted filters desirably is maintained in laminar flow throughout the room, and the flow of air from the filters desirably is, at least initially, directed vertically downwardly. Were closely positioned reflectors of known design to be employed beneath the filters and above the lights to reflect light downwardly into a clean room, the air from the filters would have to somehow pass around or through the reflectors, thereby causing an interruption in air flow and further involving a likely significant pressure drop across the reflectors.
U.S. Pat. No. 3,570,385 discloses a modular panel system for clean rooms, as does U.S. Pat. No. 3,418,915. Other patents showing various lighting structures are U.S. Pat. Nos. 3,403,614, 2,564,334, 3,090,434, 3,838,268, 3,419,714 and 2,845,855.